The publication dates of the stories in Needle in a Timestack range from 1958 to 1963, so they're from Robert Silverberg's early period, right up to the beginning of the time when he was about to become known as one of SF's more literary writers. A couple of these stories hint at what's to come, but most of them are typical fodder for the digests of the era. They're all carefully plotted, the writing is smooth and professional, but they're not in the top rank of Silverberg's work.
That doesn't mean they aren't enjoyable if you're in the mood for some old-fashioned SF, which I often am. Then they can be quite a bit of fun.
The book leads off with "The Pain Peddlers," which is one of the better stories in the book, maybe the best, and as a criticism of the media, it's almost prophetic. "Passport to Sirius" is also a story that also sounds all too possible in our own time, a story of continuous warfare and a man who wants to fight. What he finds when he gets to the front isn't at all what he expected. "Birds of a Feather" has the same plot foundation of several Silverberg stories (and many others from the era), about a ship gathering aliens for a zoo on Earth. It becomes something else, though, a con man vs. con man tale. It's entertaining but not memorable. "There Was an Old Woman" is interesting mainly for its style, which is more like that of Silverberg's later stories. A woman raises her 31 identical sons and trains each one for a specific profession. Things don't go as she expects, although she never knows it. "The Shadow of Wings" is a "first contact" story with nothing much to distinguish it. "Absolutely Inflexible" is, in spite of the collection's title, the only time travel story in the book. If you've ever read any time-travel stories, you'll see the ending of this one coming from a mile away. The setup is interesting, though. "His Brother's Weeper" is one of those stories full of SF trappings that could easily have been set in contemporary times with no SF elements at all. A supposedly dead man engaged to two women isn't dead, after all, as his brother discovers. "The Sixth Palace" is a variation on the story of the Sphinx. A massive robot is guarding a treasure trove. To get by it, you have to answer its questions. Not necessarily correctly. The twist ending kind of helps this one. "To See the Invisible Man" is another glimpse of the kind of story Silverberg was soon to become famous for, as its set in a society where people become "invisible" for the crime of coldness to their fellows. "The Iron Chancellor" is a robot-gone-wrong story that would've fit into any '50s digest. Don't trust a robot with your diet.
Some of the fun in reading these old SF stories is to see the futures imagined by the writers. In "My Brother's Weeper," there's instantaneous travel to planets millions of miles away, but when a man sitting on his patio gets a phone call, his robot butler has to fetch him into the house to talk. In most of the stories, things are recorded on tape or wire, and people still use typewriters. And of course nobody even thinks of a personal computer. This doesn't bother me in the least. I enjoyed reading the collection, but I'm a geezer and can easily flip my mind back to the '50s to read the stories. You'll have to decide for yourself.
Contet listing from ISFDB:
9 • The Pain Peddlers • (1963) • shortstory by Robert Silverberg
22 • Passport to Sirius • (1958) • shortstory by Robert Silverberg
38 • Birds of a Feather • (1958) • novelette by Robert Silverberg
63 • There Was an Old Woman— • (1958) • shortstory by Robert Silverberg
79 • The Shadow of Wings • (1963) • shortstory by Robert Silverberg
94 • Absolutely Inflexible • (1956) • shortstory by Robert Silverberg
109 • His Brother's Weeper • (1959) • shortstory by Robert Silverberg
133 • The Sixth Palace • (1965) • shortstory by Robert Silverberg
148 • To See the Invisible Man • (1963) • shortstory by Robert Silverberg
163 • The Iron Chancellor • (1958) • novelette by Robert Silverberg